What is the difference between dot notation and this : [''] while using an object in javascript

Apparently for some weird reasons I have been getting a bug on a web app and replacing it from dot notation to [''] solved it.

Observe:

from:

item.price = quantity * normal_price;

to:

item['price'] = quantity * normal_price;

Comments

[Seanmclem]

The later allows you to use variables to reference object keys. That's one way

[Abdulhafeez Abdulraheem]

This seems plausible